He is a credible and well respected historian, but
@Zauberelefant makes a good point. MHV seems to have taken the number of artillery equipment used in an artillery battalion as a literal value, but did not take the number of infantry equipment used in an infantry battalion literally as well. That is an inconsistency. Even the brightest minds make mistakes occasionally. But this debate is going nowhere, neither of you are going to convince the other that they are wrong so why keep arguing? Instead we should discuss what a better option would be to make division width less relevant. Mods have already said to stop arguing.
Overall I don't think this discussion matters a whole lot at all. I don't particularly care if the most effective divisions in the game are historical or not, I just care that the AI can put up a fight against a decent players. If the AI uses the most effective divisions, that's fine with me.
If you don't want the AI using 40 width divisions, you can play with the Expert AI 4.0 mod and set the AI to build historical templates, letting you make the game as historical as you want it to be. If you want the AI to be really hard and make only 40 width divisions disregarding historicity, you can do that too. Let paradox focus on making the game the way they want it to be, and use mods when the whole reason they exist is to tailor the player's experience to their desires.